The original 13 Reasons Why novel by Jay Asher is relatively short — the audiobook copy runs about six-and-a-half hours, about half the runtime of the Netflix series. When adapting the series to screen, the writers embraced the episodic structure of the book and split the 13 tapes into 13 episodes, but they didn't restrict themselves to the book by any means. Instead, the show expands beyond Hannah's point of view, showing new sides of her and Clay's world and humanizing the people featured on the tapes.

That's not to say the book isn't good — an author doesn't become a YA phenomenon by not being an efficient writer. But while the novel version of 13 Reasons Why features Clay viewing the world in black and white, the show deals primarily in shades of gray. There's no such thing as completely good or completely bad, and all the characters in the Netflix version of 13 Reasons Why fit somewhere on that scale — even Clay.

Asher also served as a consulting producer on the series, so none of the changes go directly against the original story or message. Despite being very different from the book in a lot of ways, 13 Reasons Why may be one of the few adaptations that surpasses its source, but fans of the book may want to keep this guide to changes handy as they watch the series. Spoilers for Netflix's 13 Reasons Why ahead, separated by groups of episodes.

Overall

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The show follows Clay's experience with the tapes over what seems to be a couple of weeks, in contrast to the book's single night. This allows the show to create a lot of scenes between Clay listening to the tapes, meaning that just about anything that isn't in the tapes or happening to Clay while he's listening to them is unique to the show.

The series also widens the scope of the story beyond Clay's experiences with the tapes to show how everyone featured on them is living in the shadow of Hannah's death. Additional plot lines include Hannah's parents suing the school for not properly dealing with bullying, the personal lives of the people that each cassette is about, and the other people on the tapes attempting to make sure that Clay doesn't reveal their contents to the world at large.

Episodes 1-3

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The book opens with Clay delivering tapes to Jenny (called Sherri on the show) after having listened to them, which the show cuts in favor of starting with Clay finding the tapes.

In the book, Justin just told others a rumor about what happened between him and Hannah, leading to slut-shaming. On the show, alongside the rumor, he shows a lewd picture taken without Hannah realizing its exact contents to a friend of his, who then sends it out to the school. This is just one way that Netflix's 13 Reasons Why adds in more modern technology to bring the original story to '17.

Tony's presence in the series — guiding those on Hannah's tapes through her requests — is introduced much earlier in the show than the book, and is a recurring thread as Clay spends weeks listening to the tapes.

The order of the tapes is switched between the book and the show, with Jessica Davis and Alex Standall being swapped in the second and third spots.

The show combines the characters of Skye, who Clay sees by herself on the bus late at night with "the girl [Clay] took shop class with" who works at Monet's. Now Skye works at Monet's, becoming a semi-regular presence in Clay's life.

Episodes 4-6

Beth Dubber/Netflix

In the scene where Marcus encourages Clay to throw a rock through Tyler's window, Marcus claims in the books that he believes he didn't do anything wrong and that Hannah is lying about what he did. On the show, Marcus claims that he didn't even listen to the full tapes — instead he just listened long enough to hear the names and passed them on.

In the book, Courtney is very comfortable with the idea of helping Hannah find out if she's being stalked, while the show depicts Courtney as curious, but not enthusiastic. During the scene in which Courtney tries to help Hannah catch her stalker, the show depicts Hannah and Courtney's evening escalating at a much slower, more hesitant pace than the book. In the original novel, Courtney acts in a more deliberately sexual way.

The characterization of Courtney as a whole takes a major change from the books. In the book, Courtney is depicted as two-faced, popular person who only used Hannah for her own benefit and threw her under the bus when it suited her. On the show, Courtney is still popular and seems to be genuinely kind, but becomes paranoid when a picture of her and Hannah kissing is sent to the entire school. In the book, Courtney spreads a rumor that Hannah has a variety of sex toys in her bedroom, seemingly for the fun of spreading rumors. On the show, Courtney tries to take any photograph-related heat off of herself by spreading a rumor that Hannah asked Courtney for a threesome with herself and a guy, and confirmed Justin's false rumors. Courtney does this because she's scared of being forced out of the closet.

When Dollar Valentine's roll around, the Clay of the book treats the whole thing as a joke — filling his form out as though he was Holden Caulfield from The Catcher in the Rye. On the show, he takes it seriously – but doesn't "get any good matches."

Clay figures out that Jenny was involved in Hannah's life through the tapes in the book, but in the television show, Sherri admits that she's on the tapes before he has a chance to listen to it.

Episodes 7-9

Beth Dubber/Netflix

There are a few subtle differences during Zach's dinner with Hannah at Rosie's, switching the gender of the waiter and showing more of Zach's tactics toward cheering Hannah up. The biggest difference is that in the book, Zach leaves his friends to sit with Hannah, while on the show, his friends have already left — leaving Zach alone with Hannah.

In the Netflix version of the story, Zach's interactions with Hannah extend beyond that one evening at Rosie's. He approaches Hannah again to try and ask her out, and her rebuttal leads Zach toward the actions that affected Hannah's life.

In the book, Hannah and Ryan meet and form a friendship our of their participating in poetry class, which changes to a poetry meeting group at the local library.

In the book, it seems that Jessica's party was Clay's first chance to hang out with Hannah, but on the show, the two had been forming a slow-budding friendship over the course of a year before the party.

In the book, the ninth tape is dedicated to Clay, but the show saves his story for later and instead focuses on Justin's second tape.

Episodes 10-13

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In the book, the student who is killed by the traffic accident that Jenny caused is a nameless student. In the show, he's Jeff, a jock who takes a liking to Clay and works to try and get him out of his shell. Jeff isn't in the books at all, but in the show he's the primary force behind Clay's attempts to actually speak to Hannah and be a more confident individual. In the books, Clay just deals with Hannah's loss, but in the show he has to deal with losing Hannah and Jeff, which pushes Clay even further into the state of anger that propels him through the series.

In the books, Hannah says that the last time that she and Clay ever talked was at that party, while on the show, Hannah has a few more conversations with Clay after what happened at Jessica's party.

The show adds a lot more to the "worst day of Hannah's life," including a stop by her old movie theater and losing her parents' bank deposit. The show also changes the location of the party where Bryce rapes Hannah from Courtney's house to Bryce's, and changes exactly what happens during the assault.

In the book, Clay only knows how Hannah died based on rumors and thinks that she overdosed on pills. The show, however, very graphically depicts Hannah slitting her wrists, and shows her parents finding her.

The final, seemingly blank, side of the last tape that Hannah leaves behind is used by Netflix's version of Clay to record a conversation with Bryce, in which he confesses to raping Hannah. In the book, the tape contains a few minutes of silence and then a solemn "Thank you," and Clay doesn't add to it.

Finally, the book ends when Clay sees Skye in the hallway at school and calls out her name after having dropped the tapes off with Jenny. On the show, Clay is supposed to leave them with Bryce, but skips him and gives them to the subject of the final tape — Mr. Porter. Then, he sees Skye in the hallway and calls out for her and they make plans to hang out before Tony drives them all into the distance.